CORBA Specification
Interface Definition Language (IDL) and Compiler
Object References
Language Mapping
CORBA Services
Interfaces
The NonStop DOM Reference Guide provides information on developing distributed object-based applications. This section introduces the concepts behind the reference information. Also see the Glossary for definitions of any terms with which you are unfamiliar.
The common Object Request Broker: Architecture and Specification Revision 2.2, updated February 1998, is a product of the Object Management Group (OMG), a consortium that includes more than 750 organizations. The focus of the OMG has been to specify the common Object Request Broker Architecture (CORBA). To describe CORBA, the OMG provides vendors with specifications rather than implementation details. The CORBA specification describes a software bus, called an Object Request Broker (ORB), that provides a foundation for distributed object computing. It allows client applications to communicate with remote objects. The CORBA specification includes a protocol for ORB interoperability called the Internet InterORB Protocol (IIOP).
This Reference Guide includes information based on the CORBA specification. Refer to the CORBA specification itself for additional information.
The CORBA specification includes a description of the Interface Definition Language (IDL). IDL allows interfaces to objects to be defined independently of the object's implementation. After defining an interface in IDL, you input the interface definition to the NonStop DOM IDL (NSDIDL) compiler. The compiler output can be compiled and linked with an object's implementation and its clients.
Refer to IDL Overview and the CORBA Specification for details about the language elements. See IDL Compiler Overview for information about the NSDIDL compiler.
An object reference is an object name that specifies a particular object. An object reference identifies the same object each time the reference is used in a request. An object may be denoted by multiple, distinct object references.
The object reference supplies the information needed to specify an object within an ORB. Both clients and object implementations indirectly specify object references through the language mapping and are separate from their actual representation.
For more information, see the Object References Overview.
All ORBs must provide the same language mapping to an object reference (usually referred to as an Object) for a particular programming language. This permits a program written in a particular language to access object references independent of the particular ORB. Language mapping may also provide convenient additional ways for the programmer to access object references.
The mapping of OMG IDL to a programming language should be the same for all ORB implementations. Language mapping includes definition of the language-specific data types and procedure interfaces to access objects through the ORB. It includes the structure of the client stub interface (not required for object-oriented languages), the dynamic invocation interface, the implementation skeleton, the object adapters, and the direct ORB interface. A language mapping also defines the interaction between object invocations and the threads of control in the client or implementation.
This document describes the IDL to C++ mapping as implemented in NonStop DOM. See IDL to C++ Mapping Overview for details.
The ORB backbone is extended with modular, add-on, system-level services that complement the functionality of the ORB and provide building blocks for business applications. The OMG has published standards for a set of common object services, including a Naming Service that enables objects to locate each other by name. NonStop DOM implements the CORBA Naming Service. See Naming Service for details about the NonStop DOM implementation. Refer also to the CORBAServices Specification for the complete standards.
CORBA services provide essential functionality for many enterprise applications. Because developers do not have to implement these core functions in each system, they can focus instead on implementing their own applications.
An interface is a set of operations that clients can use to issue requests. Interfaces are defined using the IDL. Interfaces also provide access to attributes.
This document provides reference material on the NonStop implementations of many CORBA interfaces. Refer to the relevant sections in the Reference Guide Contents and the latest CORBA specification for details on the interfaces.